A conventional transfer press having a plurality of work stations in a press machine main body is equipped with a transfer feeder and is constructed to transfer a workpiece sequentially into the successive work stations therewith.
Such a transfer feeder typically includes a pair of transfer bars which are arranged in parallel so as to extend in a feed direction. A plurality of cross bars each having a work suction means which is adapted to hold the workpiece are bridged transversely across the transfer bars to lie equidistantly spaced apart from one another in the feed direction. In operation, the transfer bars are driven two dimensionally both in the feed direction and in the lift direction to allow the workpiece to be transferred into and from one of the work stations into another in sequence.
In a transfer feeder as described above, a feed cam is rotated by a power taken from the press main body to cause a feed lever to be swung so that the above mentioned transfer bars which are mechanically coupled to the feed lever may be driven in the feed direction. With such a construction adopted, the transfer feeder of this type provides a feed stroke that is definitely determined by a particular profile of the feed cam, which therefore cannot be changed without exchanging the feed cam, and hence has been found to be inconvenient.
In order to take into account such an inconvenience, there has been proposed, e. g., in Japanese Unexamined Patent Publication No. Sho 61-115633 or Japanese Unexamined Utility Model Publication No. Sho 64-5719, a workpiece transfer apparatus that is designed to allow the feed stroke of a cross bar to be altered.
A workpiece transfer apparatus as described in these publications includes a pair of feed bars (which correspond to the transfer bars mentioned) extending in the feed direction each of which is provided with a slide member that is slidable in the feed direction. A cross bar is there bridged transversely across a pair of such slide members which are juxtaposed with each other to provide a feed stroke that can be rendered variable when they are displaced in the feed direction by a cylinder drive unit to allow them to move relative to the feed bars.
A workpiece transfer apparatus as proposed in these publications has, however, been found to be yet inconvenient because of the construction in which a guide means for guiding the feed bars in the feed direction and a guide means for guiding the slide members slidably need to be arranged to be vertically separate. This requires the structure for the both placed to be greater in height to the extent that the field of view and the visibility for the inside of the press machine may substantially be lost by the slide members, the cylinder drive unit and so forth.
An increase in height of the press machine body also results in an increased backlash or looseness thereof in the vertical direction, which tends to cause the cross bars to be vibrated, bringing about an accidental fall of the work from the work suction means and further a failure in or an incorrectness of feed.
A transfer feeder must also be used wherein the path in which a workpiece is transferred (path line) can in height be varied in several levels depending on the sizes and shapes of particular workpieces. If the path line is to be altered in the transfer feeder, it, too, has been found to be defective because of the development of an error in feed stroke and the inability to suck a proper position of a workpiece with the suction means for reasons as mentioned below.
Specifically, the structure in which a feed lever and a cross bar carrier are coupled together by a linkage having a given length causes a change in height of the cross bar carrier with the feed lever halted to result in a circular motion of the point at which the link member and the cross bar carrier are pivotally connected together about the point at which the link member and the feed lever are pivotally connected together.
A change in height of the path line may, therefore, cause the cross bar carrier to be displaced in the feed direction, bringing about inconveniences represented by the development of an error in feed stroke. Consequently, the suction means becomes unable to attract and thereby to hold a workpiece as properly positioned, which thus tends to be incorrectly fed in the path line or cannot be transferred into a work station accurately at a given location.
In an attempt to resolve such problems, a corrective apparatus for a transfer feeder has been proposed in which a height adjustment means is provided at a site where the link member and the cross bar carrier are coupled together so that if the path line is varied in height the pivotal point at which the link member and the cross bar carrier are connected together may be vertically adjusted in position by the height adjustment means, thus that there may be no error in feed stroke.
The corrective apparatus proposed has yet been found to be disadvantageous, however, in that it involves a substantial increase in cost arising from the need for a height adjustment motor means and it is also inconvenient for the requirement of a space for accepting the height adjustment means where the link member and the cross bar carrier are coupled together.
It is accordingly an object of the present invention to eliminate these disadvantages in the prior art and to provide a variable feed stroke feeder apparatus for a transfer feeder which permits the feed stroke to be altered without difficulty and assures a good visibility in the press machine body, yet without permitting a change in height of the path line to develop an error in feed stroke.